The invention relates to a magnetic head having a head face and comprising a head structure composed of thin layers and provided with a transducing element, in which different materials in different areas are present in the head face.
A magnetic head of this type is known from JP-A 63-37811 (herewith incorporated by reference). The known magnetic head has a thin-film structure provided on a substrate and comprises a magnetic yoke with a magnetoresistive element and a transducing gap. The magnetic head also has a head face in which the transducing gap and magnetic flux guides for guiding magnetic information towards the magnetoresistive element terminate. The head face of the known magnetic head is used for guiding a magnetic record carrier, particularly a magnetic tape.
In magnetic heads which have a layer structure, soft materials, notably soft-magnetic materials of flux guides, for example permalloy, occur in addition to relatively hard materials, notably substrate materials, for example Al2O3/TiC. Due to the abrasive effect of the record carrier moving along the head face during operation, the relatively soft materials may wear on the head face, which results in a hollowing of the layer structure of the head face. Such a hollowing leads to a larger distance between the record carrier and the layer structure and hence to a reduced transfer of information from the record carrier to the magnetic head. Consequently, a long lifetime cannot be guaranteed for the known magnetic head whose head face also serves as a tape contact face.
It is known per se to provide wear-resistant layers on the head faces of magnetic heads in order to inhibit wear. It is known from IBM Technical Disclosure Bulletin, vol. 11, no. 10, March 1969, pp. 1199 (herewith incorporated by reference) to provide Cr2O3 by means of flame plating on heat-resistance magnetic heads for forming wear-resistant layers. JP-A 66-73917 (herewith incorporated by reference) proposes to provide core limbs of permalloy comprising Cr with a layer of Cr oxide having a thickness of more than 0.5 xcexcm and to form a layer of Cr oxide by means of sputtering on core limbs of permalloy not comprising Cr. EP-A 0 123 826 (herewith incorporated by reference) proposes to provide the head face of a magnetic head with a sputtered layer of titanium carbide, chromium carbide or titanium nitride which is thinner than 0.2 xcexcm. However, magnetic heads whose head faces have a wear-resistant layer have the problem that the transfer of information from the record carrier to the magnetic head is worse than in corresponding magnetic heads without a wear-resistant layer on the head face. In order that more favourable output signals are still achieved during operation, it is required that the wear-resistant layer should not be made thicker than is strictly necessary due to the wear-inhibiting function. Thin wear-resistant layers, notably thinner than 100 nm, are generally not gas and moist-proof so that corrosively reacting substances, notably from the record carrier, can reach the head face via pores in the wear-resistant layer. Notably soft-magnetic materials such as NiFe alloys are readily affected by corrosively reacting substances, resulting in a decrease of the transfer of information from the magnetic tape to the transducing element. It has been found that many magnetic tapes contain, inter alia chlorine, and that during scanning of these magnetic tapes Cl ions diffuse from the magnetic tapes into the head faces of the magnetic heads where they cause local corrosion.
It is an object of the invention to improve the magnetic head described in the opening paragraph in such a way that it has a wear-resistant and corrosion-resistant head face.
The magnetic head according to the invention is characterized in that the head face is provided with a first layer of a material which is more sensitive to corrosion than said materials in the head face, and the first layer is provided with a second layer of a wear-resistant material which is more insensitive to corrosion than the material of the first layer.
The second layer, which constitutes a contact face for cooperation with a record carrier, protects the magnetic head according to the invention from abrasive and corrosive wear, while the first layer present between the head face and the second layer protects the magnetic head from corrosively reacting substances such as chlorine originating from the record carrier. It has also been found that the adhesion of wear-resistant materials to materials occurring in the head face can be improved by suitable choice of the material of the first layer; in other words, the first layer may also serve as an adhesive layer.
To ensure a favourable signal transmission from the record carrier to the transducing element and/or from the transducing element to the record carrier, said layers should have a minimal thickness. Favourable results were achieved with magnetic heads according to the invention, whose first layer had a thickness of between 1 nm and 20 nm and whose second layer had a thickness of between 10 nm and 100 nm. However, a magnetic head is preferred whose first layer has a thickness of less than 5 nm and whose second layer has a thickness of less than 60 nm, because only very limited output losses occur in such cases.
An embodiment of the magnetic head according to the invention is characterized in that the material of the first layer mainly comprises a metal from the group of Ti, Zr, Hf, V, Nb, Ta, Cr, Al, Zn. All the metals of this group are non-magnetic metals having lower standard reduction potential, xe2x80x94Exc2x0 values in accordance with the U.S. definition, than Fe; thus, they are less noble than Fe as well as Fe alloys, for example an NiFe alloyxe2x80x94permalloyxe2x80x94. Thus, soft-magnetic flux guides of permalloy terminating in the head face are protected from corrosion by the material of the first layer. The metals may be provided on the head face by means of known deposition methods, particularly physical or chemical vapour deposition such as sputtering or CVD.
An embodiment of the magnetic head according to the invention is characterized in that the material of the second layer is one of the materials from the group of chromium oxide, chromium nitride, hafnium nitride, titanium nitride, chromium carbide, titanium carbide, tungsten carbide, diamond. All these materials have good wear-resistant properties and adhere satisfactorily to the metals of the first layer. The materials may be provided on the first layer by known techniques such as sputtering deposition, vapour deposition or CVD. For process reasons the following combinations of materials for the first and second layers are preferred: titanium and titanium nitride or titanium carbide; hafnium and hafnium nitride; chromium and chromium oxide or chromium nitride or chromium carbide.
An embodiment of the magnetic head according to the invention is characterized in that the chromium oxide is mainly Cr2O3, the material of the first layer being Cr. This magnetic head according to the invention has a wear-resistant contact face formed by the layer mainly comprising Cr2O3 for cooperation with a record carrier, particularly a magnetic tape. At a layer thickness of 10 nm to 100 nm a favourable signal transmission between the record carrier and the transducing element is ensured. It has also been found that the contact face has a good wear resistance, not only in the temperature range between 5xc2x0 C. and 85xc2x0 C., but also at temperatures in the range between 5xc2x0 C. and xe2x88x9220xc2x0 C. This is particularly important for magnetic heads which are used in portable apparatuses and in magnetic scanning devices intended for outdoor use, such as car radio cassette recorders.
It has been found by experiment that a layer of eminent quality mainly comprising Cr2O3 on the head face can be obtained by sputtering. Already at layer thicknesses of less than 60 nm, high wear resistances are found to be achievable by means of sputtering. A further advantage of the sputtered wear-resistant layer mainly comprising Cr2O3 is that it can be formed at temperatures of less than 300xc2x0 C. The magnetic properties of magnetic materials present in the layered head structure will then remain unaffected during formation of this layer. A wear-resistant layer mainly comprising Cr2O3 and provided on the head face by means of sputtering yields a magnetic head according to the invention which supplies favourable output signals during operation and is suitable for use at relatively low temperatures and, moreover, has a long lifetime.
It has been found by experiment that a layer having a thickness of approximately 5 nm mainly comprising Cr and preferably provided by means of sputtering is sufficient to inhibit corrosion of the head face and to ensure a satisfactory adhesion of the layer mainly comprising Cr2O3 to the head face.
The invention also relates to a method of manufacturing a magnetic head according to the invention, whose first layer mainly comprises Cr and whose second layer mainly comprises Cr2O3. In this connection the invention has for its object to provide a method which is as simple as possible for manufacturing such a wear-resistant magnetic head.
The method according to the invention is characterized in that a first layer mainly comprising Cr is formed on the head face, at least on the head structure by sputter deposition, and a second layer mainly comprising Cr2O3 is formed on the first layer also by sputter deposition.
An embodiment of the method according to the invention is characterized in that sputtering is performed with a chromium target without oxygen addition until the first layer is formed, whereafter oxygen is supplied for forming the second layer. It has been found that the oxygen can be supplied after the formed layer mainly comprising Cr has a thickness of several nanometres. It has also been found that, provided it is not extremely low, the oxygen pressure has no substantial influence on the composition of the formed wear-resistant layer mainly comprising Cr2O3, which renders the properties of this wear-resistant layer independent of small process variations. Due to the reliability of the method, sputtering in the presence of oxygen need only to take place until the formed layer mainly comprising Cr2O3 has a thickness of approximately 60 nm.